As I understand your question you want to replace 1 with On and 0 with Off in your gridview.
You can do it like this.
for (int i = 0; i < GridView1.Rows.Count; i++)
{
if (GridView1.Rows[i].Cells[0].Text == "1")
GridView1.Rows[i].Cells[0].Text = "On";
else
GridView1.Rows[i].Cells[0].Text = "Off";
}
If this doesnot solve your problem. please explain clearly.